Field of the Invention
The invention generally relates to maintaining or restoring potato turgidity, and/or to preventing greening and/or to treating interior fungal and bacterial diseases of root vegetables by the application of α,β-unsaturated aliphatic aldehydes and ketones, C3 to C14 aliphatic aldehydes and ketones, and/or C3 to C7 aliphatic primary and secondary saturated and unsaturated alcohols. In particular, root vegetables (such as potatoes) are treated prior to or during storage to limit damage due to loss of turgidity, greening and/or disease.
Background of the Invention
Following harvest, potato tubers undergo a natural period of dormancy during which sprout growth is inhibited by endogenous hormones. As tubers emerge from dormancy and begin to sprout, respiration increases, starch is catabolized to sugars, which leads to weight loss and loss of turgidity. The result is a decrease in overall quantity and quality of tubers destined for fresh and processing markets. One method to preserve tuber turgidity is to have good sprout control. Hence, efforts have been made to inhibit sprouting through chemical or physical means to preserve quality during storage. The sprout inhibitors registered for use on potatoes in the United States include CIPC (also known as chlorpropham, Sprout Nip®, etc.), maleic hydrazide (MH), DMN (also known as dimethylnaphthalene, 1,4SIGHT®, 1,4SEED®, 1,4SHIP®), DIPN (diisopropylnaphthalene, Amplify®), and clove oil (Biox-C®; Sprout Torch™). Except for MH, which is applied pre-harvest to actively growing plants, all inhibitors are applied post harvest when tubers are in the storage bin.
CIPC is the most effective and most widely used potato sprout inhibitor. This chemical agent is most often applied as a thermal aerosol fog into potato storages after wound-healing and prior to sprouting. In the Pacific Northwest, this is usually in November or December, before dormancy has ended. The chemical is fogged into storage at the recommended rate of 1 lb chlorpropham/600 cwt. One gallon of CIPC aerosol grade will treat 4200 cwt (210 tons) of potatoes. While CIPC can inhibit sprouting and extend the storage life of table-stock and processing potatoes for the storage season with one or more applications, it does not promote or maintain tuber turgidity or prevent tuber greening. One of the drawbacks with CIPC is that when the tubers are treated in storage before proper wound healing and suberization of the potatoes has taken place, CIPC can impede these natural processes and therefore increase storage disease incidence.
While other potential sprout suppressant agents have been identified (e.g. aromatic aldehydes and alcohols, methyl esters of rape oil, carvone, jasmonates, spearmint and peppermint oils), none appear as effective as CIPC. 1,4 SIGHT™ (94.7% DMN=1,4-dimethylnaphthalene) is a naturally-occurring chemical agent that is also registered for sprout control (see U.S. Patent Publication 2001/0021406), but it tends to be less effective than CIPC and is considered a dormancy enhancer.
Other alternative sprout inhibitors are described in U.S. Patent Publication 2007/0135307 to Olson which describes sprout inhibition with carbetamide, pronamide, ethofumesate, mefluidide, paclobutrazol, 2,4 DB, and 2,4 DP, and in U.S. Patent Publication 2007/0078058 which shows the use of MCPP to inhibit sprouting. Issued U.S. Pat. No. 5,139,562 (Vaughn, et al.) discusses the use of the oxygenated monoterpenes 1,4-cineole, 1,8-cineole, fenchone, and menthol to inhibit tuber sprouting.
Other natural volatile sprout inhibitors have been identified. Carvone (derived from caraway seed) is commercially available for use on potatoes in the Netherlands (Hartmans et al 1995. The following US patents describe the use of various compounds for the inhibition of potato sprout formation: U.S. Pat. No. 5,436,226 to Lulai, et al. (Jul. 25, 1995) describes the use of jasrnonates; U.S. Pat. No. 5,635,452 to Lulai et al (1997) describes the use of aromatic acids, U.S. Pat. No. 6,855,669 to Knowles and Knowles (2005) describes the use of α,β unsaturated aldehydes and ketones, U.S. Pat. No. 8,258,081 to Knowles et al. describes the use of C3 to C14 aliphatic aldehydes, ketones and primary and secondary C3 to C7 aliphatic alcohols to inhibit sprouting of potato tubers, U.S. Pat. No. 5,580,596 to Winkelmann et al. (Dec. 3, 1996) describes the use of rape seed oil and certain long-chain alcohols, either alone or in combination; U.S. Pat. No. 5,139,562 to Vaughn et al., (Aug. 16, 1992) describes the use of volatile monoterpenes (e.g. from eucalyptus, peppermint, spearmint, etc.); and U.S. Pat. No. 8,329,618 B1 teaches that certain essential oils can promote tuber hardness as well, and U.S. Pat. No. 5,129,951 to Vaughn et al., (Jul. 14, 1992) describes the use of aromatic aldehydes and alcohols. In addition, Vokou et al. (1993) have demonstrated that the essential oils from a multitude of herbs (e.g. sage and rosemary) possess sprout inhibiting activity in potatoes.
Softening of the potato during storage significantly decreases or eliminates its commercial value. Thus, identification of agents that can improve turgidity of potatoes are needed in the industry. Furthermore, identification of agents that restore turgidity, whereby an otherwise stored flaccid potatoes absorb moisture and become “hard or firm” to the touch, are of significant commercial interest.
Another possible problem that occurs in association with growing, harvesting and storing potatoes is “greening” which occurs upon exposure to light. Greening adversely affects both the appearance and nutritional qualities—and even the safety—of potatoes, which at one time were considered to be poisonous. In fact potatoes do contain poisonous compounds in the form of glycoalkaloids such as solanine. Such toxins are always present near the surface of the potato, with the highest concentrations in the eyes or sprouts. These toxins are a natural defense mechanism of the plant, and are harmless when ingested in very small quantities, but ingestion of high levels causes headaches, diarrhea, cramps, and, in severe cases, coma and death. The U.S. National Toxicology Program recommends consumption of at most 12.5 mg of solanine from potatoes per day.
Solanine levels in potatoes vary somewhat depending on the variety, age, maturity, storage temperature, etc., but the levels are significantly increased upon exposure to light. Light also causes chlorophyll production and the resulting development of a green skin color; hence, the degree of “potato “greening” is an indirect indicator of the development of toxins such as solanine. Generally, the greener the potato, the more likely that high concentrations of solanine and other glycoalkaloids are present. Commercially grown potatoes are selected so as to have low initial concentrations of solanine, but post-harvest exposure to light can rapidly increase these levels to ten or more times the original value. For example, grocery store fluorescent lighting can induce potato greening in as little as 12 hours. If a potato is more than 5 percent green, the U.S. Department of Agriculture considers the potato damaged and less than US Grade #1.
Unfortunately, there are currently no products available for preventing or slowing “greening” of potatoes and this area is also of significant commercial interest.
In addition, with respect to the treatment of fungal and bacterial diseases in stored produce, it is known that e.g. trans-2-hexenal inhibits mold and bacterial growth on harvested plant commodities (Corbo et al., J. Agric. Food Chem. 48:2401-2408 (2000); Archbold et al., HortScience 34:705-707 (1999)). US patent application 20130266670 (Sardo) teaches that essential oil exhibit fungicidal, bactericidal and/or antioxidative properties. However, these references teach only the control of surface fungal and bacterial pathogens, i.e. the compounds described therein are used as surface sanitizers, whereas diseases that infect the interior of produce (e.g. Fusarium dry rot of the potato), and are a huge commercial problem, are not addressed. There is thus still a pressing need in the art to identify and develop agents that prevent, treat, limit and/or cure fungal and bacterial infections (e.g. of root vegetables) that occur within the root itself. Control of such pathogens has significant commercial interest as these pathogens become particularly economically important as they frequently occur during storage. It would be especially desirable to have available agents that can treat and/or eliminate or lessen internal infections that are already present e.g. within a tuber before treatment is begun.